Darwin’s finches are highly adaptable and able to cope with the unpredictable characteristics of the Galápagos Archipelago. They show an extraordinary number and diversity of feeding innovations, including consumption of novel food types and foraging behaviours (reviewed in ref. 1). These feeding innovations are novel in the sense that such behaviour patterns are unusual for passerines and it is likely that they evolved after their ancestors colonised the islands. It has been proposed that the ability to innovate so readily has contributed to the adaptive radiation of this clade . Since the permanent colonisation of the Islands by humans, Darwin’s finches have been exposed to a new set of risks and challenges, in particular exotic parasites and pathogens that reduce the survival and reproductive success of the birds. Here we report for the first time an innovation of this species group that is outside the feeding context: in 2012 we observed a warbler finch (Certhidea olivacea) tearing off the tips of leaves of the endemic Guayabillo tree, Psidium galapageium, and rubbing them on its feathers. Over the last
four years, we have observed ten incidents of this behaviour in four species of Darwin’s finches (see Table 1). We have identified two different methods: (1) sponge method, the bird threads a piece of leaf through its feathers and (2) lotion method, the bird chews the leaf first and applies the mashed leaf to its feathers. In all instances, the birds used P. galapageium leaves, although this tree species occurs at low densities in the highlands of Santa Cruz Island
where the observations were made.

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